DuPont™ Vespel® S

Vespel® S refers to a group of virtually non-meltable aromatic polyimides (PI). These materials made from the original DuPont™ Vespel® have outstanding high-temperature properties. They are characterised by a wide range of applications from cryogenic temperatures to well over 400°C for short periods. The mechanical properties of Vespel® S grades remain virtually stable over the entire temperature range.

The materials have a low coefficient of thermal expansion, high wear resistance and a low tendency to creep. They are also characterised by high purity and low outgassing behaviour.

Main features:

• Heat deflection temperature > 300°C
• High wear resistance
• High purity and low outgassing behaviour

The Vespel® S polyimide group includes the semi-crystalline Vespel® SP and the mechanically stronger and thermally even more stable Vespel® SCP.

The various Vespel® S grades are resistant to most solvents, but are attacked by strong acids and alkalis. Like most polyimides, the Vespel® S grades are hygroscopic and therefore not resistant to hydrolysis. However, the materials are well suited for vacuum applications. They hardly outgas even in a high vacuum and have good dry-running properties.

The disadvantage of Vespel® S grades is that they cannot be processed thermoplastically. Components must therefore either be machined from semi-finished products or, for larger quantities, moulded directly using a press-sintering process.

The semi-crystalline Vespel® SP has no detectable glass transition temperature or other softening points below a decomposition temperature well above 400°C.

The material can be used at temperatures of up to 300°C, and even up to almost 500°C for short periods. Due to these thermal properties, Vespel® SP behaves almost like a thermosetting plastic and shows an almost linear change in mechanical properties over the entire temperature range of use. Special material types modified with graphite and fluorocarbon are available for use in wear applications. The following Vespel® SP grades are available as clamped or directly moulded components.

• Vespel® SP-1 (PI) is the unfilled standard grade of the Vespel® SP series with a balanced property profile. The material has good electrical insulation properties and is well suited for vacuum applications due to its high degree of purity. > Data sheet
   
• Vespel® SP-21 (PI GR15) is a graphite-modified PI grade that can also be used for dry running. The graphite content leads to a reduction in the coefficient of friction and an improvement in wear resistance and heat ageing. The plastic is ideal for highly stressed bearing parts, thrust washers and seals. > Data sheet
   

• Vespel® SP-211 (PI GR15 TF10) is a PI grade that has been developed for dry-running sliding applications. The plastic has been optimised in particular for its sliding and wear properties and offers the lowest static friction of all pure aromatic PI grades. Data sheet
   
• Vespel® SP-22 (PI GR40) is a graphite-modified polyimide grade with a significantly higher graphite content than SP-21. The plastic has the lowest coefficient of thermal expansion of all aromatic PIs, combined with high creep resistance. Data sheet
   
• Vespel® SP-3 (PI MO) is a PI modified with molybdenum disulphide (MoS2), which has been developed especially for dynamic or tribological applications in a vacuum. SP-3 offers the best dry-running properties.> Data sheet

Compared to Vespel® SP, Vespel® SCP is characterised by significantly higher mechanical strength over a wide temperature range. At temperatures up to over 250°C, it is superior to the polyimides known to date. The strength only drops significantly above 300°C.

Vespel® SCP is also superior to most plastics in terms of dimensional stability. The expansion coefficient of Vespel® SCP-5050, which is highly filled with graphite, is comparable to that of stainless steel. In addition, Vespel® SCP shows better chemical resistance than the known polyimides and is also superior to them in terms of resistance to thermal-oxidative degradation.

The following Vespel® SCP types are available as clamped or directly moulded components for use as sealing or sliding elements.

• Vespel® SCP-5000 (PI) is the unfilled standard grade, which differs from the Vespel® SP grades due to its improved thermal stability, chemical resistance and dimensional stability. At the same time, this material is highly pure and hardly outgasses. Data sheet

• Vespel® SCP-5009 (PI GR) is a graphite-modified grade for elevated temperatures with improved compressive strength. At the same time, this material has excellent sealing properties and a low coefficient of friction in dry running. Data sheet
   
• Vespel® SCP-50094 (PI GR) is the tribological standard grade with high wear resistance. This material combines the well-known good properties of Vespel® SP-21 with even greater thermal stability. Data sheet
   
• Vespel® SCP-5050 (PI GR) is a tribologically modified special grade with excellent sliding properties, which is characterised by an extremely low coefficient of thermal expansion due to the high graphite filling. Data sheet